CVE-2026-64009xfrm: Check for underflow in xfrm_state_mtu
- 7.8HighCVSS base score
- 0.14%Exploitation in 30 daysEPSS · top 96% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
In the Linux kernel, the following vulnerability has been resolved: xfrm: Check for underflow in xfrm_state_mtu Leo Lin reported OOB write issue in esp component: xfrm_state_mtu() returns u32 but performs its arithmetic in unsigned modulo-2^32 space using an attacker-influenced "header_len + authsize + net_adj" subtracted from a small "mtu" argument. A nobody user can install an IPv4 ESP tunnel SA with a large authentication key (XFRMA_ALG_AUTH_TRUNC, e.g. hmac(sha512), 64-byte key, 64-byte trunc), configure a small interface MTU (68 bytes), and set XFRMA_TFCPAD to a large value. When a single UDP datagram is then sent through the tunnel, xfrm_state_mtu() underflows to a near-2^32 value, and esp_output() consumes it as a signed int via: padto = min(x->tfcpad, xfrm_state_mtu(x, mtu_cached)) esp.tfclen = padto - skb->len (assigned to int) esp.tfclen ends up negative (e.g. -207). It is sign-extended to size_t when passed to memset() inside esp_output_fill_trailer(), producing a ~16 EB write of zeroes at skb_tail_pointer(skb). KASAN logs it as "Write of size 18446744073709551537 at addr ffff888...". Check for underflow and return 1. This causes the sendmsg attempt to fail with ENETUNREACH.
Timeline
ID reserved
By Linux
Published
- 3 months later
· 3 months later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| LinuxCNA (assigner) | 3.1 | High7.8 | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
| NVDNVD · Modified | 3.1 | High7.8 | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
- EPSS (exploitation in 30 days)
- 0.14% · top 96% of all CVEs (13 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.8.
Affected products
- affected c5c2523893747f88a83376abad310c8ad13f7197 – < 8014f70c4e6e5ab101ae3860a614e65e988372e3
- affected c5c2523893747f88a83376abad310c8ad13f7197 – < 1021d2877b689a648b27815c854557a917122e93
- affected c5c2523893747f88a83376abad310c8ad13f7197 – < 2a41b1b31c61c52b972278ce1732a1443f5e89ed
- affected c5c2523893747f88a83376abad310c8ad13f7197 – < fccd685b32df5aaf6bad4381eeda216468e283f0
- affected c5c2523893747f88a83376abad310c8ad13f7197 – < 820e501be8aee4b365d218d83227b314309c5fda
- affected c5c2523893747f88a83376abad310c8ad13f7197 – < 82ac903e0b519849647657b8c48d21237ada06a2
- affected c5c2523893747f88a83376abad310c8ad13f7197 – < 3db50ceeacb52806d8fe86fb1dfe944df0b9f789
- affected c5c2523893747f88a83376abad310c8ad13f7197 – < 742b04d0550b0ec89dcbc99537ec88653bd1ad90
- affected 2.6.22
- unaffected < 2.6.22
- unaffected 5.10.259 – ≤ 5.10.*
- unaffected 5.15.210 – ≤ 5.15.*
- unaffected 6.1.176 – ≤ 6.1.*
- unaffected 6.6.143 – ≤ 6.6.*
- unaffected 6.12.93 – ≤ 6.12.*
- unaffected 6.18.35 – ≤ 6.18.*
- unaffected 7.0.12 – ≤ 7.0.*
- unaffected 7.1 – ≤ *
References
References8
- https://git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3 (opens in a new tab)
- https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93 (opens in a new tab)
- https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed (opens in a new tab)
- https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0 (opens in a new tab)
- https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda (opens in a new tab)
- https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2 (opens in a new tab)
- https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789 (opens in a new tab)
- https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90 (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-45582 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-64009)Record last updated .